This invention relates to a piezoelectric acoustic device, and more particularly to a piezoelectric acoustic device in the form of a piezoelectric speaker, a piezoelectric buzzer or the like which is suitable for use for an electronic equipment such as a portable telephone or the like.
A piezoelectric acoustic device which has been conventionally known in the art is disclosed in U.S. Pat. No. 4,079,213 and U.S. Pat. No. 4,989,302. The conventional piezoelectric acoustic device disclosed includes a casing constituted of a combination of a first casing half and a second casing half, as well as a piezoelectric vibrator received in the casing. The piezoelectric vibrator includes a vibrating plate which is made of a metal material and has an outer peripheral portion interposedly held between the first casing half and the second casing half. Another piezoelectric acoustic device is also proposed which is constructed in substantially the same manner as that described above except that a vibrating plate is joined at an outer peripheral portion thereof to a casing by means of an adhesive.
Unfortunately, the adhesive before curing is pasty and exhibits flowability or fluidity, resulting in flowing on a metal vibrating plate while spreading inwardly in a radial direction thereof. Thus, after the adhesive is cured, it deteriorates vibration of the outer peripheral portion of the metal vibrating plate, to thereby reduce a substantial diameter of the metal vibrating plate. For example, when the adhesive spreads by 0.5 mm inwardly in the radial direction of the metal vibrating plate, the metal vibrating plate is reduced by about 1.0 mm in substantial diameter thereof.